Field of the Invention
The present invention generally relates to an electric drive motor assembly for a wheel. More specifically, the present invention relates to a drive assembly for a wheel of a vehicle having an electric traction battery.
Background Information
Several different electric motor arrangements exist to drive wheels of an electric vehicle. One example is a center-mounted motor disposed between a pair of wheels to drive both wheels. The center-mounted motor occupies a large volume because it is centrally disposed and requires drives shafts extending outwardly to each wheel, thereby occupying a majority of the space between the wheels. Further, because of this space inefficiency, the center-mounted motor is not conducive to providing a four-wheel drive vehicle. Similar to the center-mounted motor is an offset center-mounted motor in which the motor axis is offset from the rotation axis of the two wheels being driven. The same disadvantages of the center-mounted motor are associated with the offset center-mounted motor.
Another conventional motor used to drive wheels of an electric vehicle is a wheel hub motor, which is directly connected to a wheel hub such that a drive shaft is not required. Although space is saved with the configuration of the wheel hub motor, the unsprung mass is increased because the wheel hub motor is not supported by the vehicle's suspension. Due to the increased unsprung mass, the vehicle's ride and handling ability is lessened. Additionally, as the rotational mass of the wheel increases, more energy is required to overcome inertia and rotate the tires or to stop rotation of the tires. Moreover, the larger unsprung mass results in passengers experiencing a bumpier ride because the unsprung mass is not supported by the vehicle's suspension.
Further, because more energy is required to rotate and stop the tires, a larger motor is required. However, due to the wheel hub motor being disposed in the wheel hub, reduction gear assemblies cannot typically be used to reduce the size and necessary output of the required motor.
An offset wheel hub motor is similar to the wheel hub motor, except that the motor axis is offset from the rotation axis of the wheel. This arrangement is sometimes deployed to better enable packaging of the brake assembly inside the wheel. The same disadvantages of the wheel hub motor are associated with the offset wheel hub motor.
The electrical connection to a wheel hub or offset wheel hub motor necessarily translates through a large displacement as it must move with the wheel. This requires measures to ensure reliable operation, such as a longer length of wiring and added protection of the wiring from abrasion. Accordingly, a need exists for an improved electric drive motor assembly for a wheel.